FIG. 1 illustrates a schematic view of a white light emitting component disclosed in U.S. Pat. No. 5,998,925. Referring to FIG. 1, a white light emitting component 1 includes a casing 11, a gallium nitride compound light emitting diode chip that is capable of emitting a blue light, and a fluorescent material 13. The fluorescent material 13 is mixed into the coating resin 14 and is configured for absorbing a part of the blue light emitting from the gallium nitride compound light emitting diode chip to emit a green light. Thus, the blue light and the green light are mixed to form a white light to output.
FIG. 2 illustrates a spectrogram of a white light emitting component with high color render index disclosed in U.S. Pat. No. 5,851,063. Referring to FIG. 2, the white light emitting component includes a light emitting diode for emitting a light in the blue wavelength range (455-490 nm), a light emitting diode for emitting a light in the green wavelength range (530-570 nm) and a light emitting diode for emitting a light in the red wavelength range (605-630 nm). The white light emitting component having an optimized color render index (e.g., the color render index is more than 80) can be achieved by selecting a suitable chromaticity of the wavelength range of each of the three light emitting diodes.
Additionally, U.S. Pat. No. 6,351,069 discloses a white light emitting component with high color render index and uniform chromaticity. The white light emitting component includes a light emitting diode for emitting a blue light and two fluorescent materials. The light emitting diode for emitting the blue light is, for example, a gallium nitride based light emitting diode chip. The two fluorescent materials are configured for absorbing a part of the blue light to emit a green light and a red light respectively. The blue light, the green light and the red light with different wavelength are mixed to form a white light to output. Thus, the white light emitting component with high color render index and uniform chromaticity can be obtained.
FIG. 3 illustrates a schematic view of a white light emitting component with high color render index and high light emitting efficiency disclosed in U.S. Pat. No. 6,234,648. Referring to FIG. 3, in order to overcome the shortcomings of the above-mentioned white light emitting components, a white light emitting component 20 includes a gallium nitride based light emitting diode 21 for emitting a blue light, a light emitting diode 22 for emitting a red light, and a fluorescent material 23. The fluorescent material 23 is capable of absorbing a part of the blue light emitting from the gallium nitride based light emitting diode 21 to emit a green light. The blue light, the green light and the red light with different wavelength are mixed to form a white light to output. Thus, the white light emitting component with high color render index and high light emitting efficiency can be obtained.
FIG. 4 illustrates a schematic view of a light emitting device disclosed in U.S. application 20090109151. Referring to FIG. 4, in order to increase the color render index of a white light emitting component driven by an alternating current (AC) power, a white light emitting device 40 includes two groups of light emitting diodes driven by the AC power 41, 42 and a coating resin mixed with a fluorescent material 43. The two groups of light emitting diodes driven by the AC power 41, 42 can emit two different lights. In a first example, the white light emitting device 40 can includes a group of light emitting diodes driven by the AC power for emitting a blue light and a group of light emitting diodes driven by the AC power for emitting a green light. The coating resin is mixed with a fluorescent material for emitting a red light, and is disposed on the group of light emitting diodes driven by the AC power for emitting the blue light.
In a second example, the white light emitting device 40 can includes a group of light emitting diodes driven by the AC power for emitting a blue light and a group of light emitting diodes driven by the AC power for emitting a red light. The coating resin mixed with a fluorescent material for emitting a light in a wavelength range between the blue light wavelength and the green light wavelength. The coating resin is disposed on the group of light emitting diodes driven by the AC power for emitting the blue light. U.S. application 20090109151 discloses a method to increase the color render index. However, the light conversion efficiency of the fluorescent material that absorbs the blue light to emit the red light (600-630 nm) is still low. Thus, although the first example can increase the color render index of the white light emitting device, the light emitting efficiency of the white light emitting device can not be increased effectively. Although the second example can increase the color render index of the white light emitting device effectively and can avoid the decrease of the light emitting efficiency of the light emitting device, the light emitting diodes driven by the AC power for emitting the blue light and the light emitting diodes driven by the AC power for emitting the red light are separately disposed.
Therefore, a light emitting component with high light emitting efficiency as well as properties of high driving voltage, high color render index (CRI) and concentrated optical density is desirous.